1. Field of Invention
The present invention relates to etching processes for use in the production of semiconductor devices.
2. Description of Related Art
The number of transistors that have been integrated in semiconductor integrated circuits has become higher and higher in recent years, which requires an etching process capable of forming fine patterns with a high etching selectivity. In order to form fine patterns by etching, it is necessary to form fine photoresist patterns that are used as masks in the etching processes. The focus depth in the photolithography process becomes shallower for a finer pattern, and a thinner photoresist (hereinafter simply referred to as xe2x80x9cresistxe2x80x9d) film should be used.
Further, etching should be performed while controlling the shape of the patterns formed by the etching. In order to control the pattern shape, the sidewalls of the layer subject to etching should be protected. To this end, a process is employed, which comprises etching the resist layer and depositing the etched resist materials on the sidewalls of the layer subjected to etching. In this case, if the initial thickness of the resist layer is not sufficient, the resist film ingredients disappear during the etching, and the shoulders of the etched patterns are faceted. Namely, pattern shape degradation occurs. Because the protection of such sidewalls should be increased for finer patterns, the thickness of the resist film is on a trade-off relationship between the precision in the photolithography process and the pattern-shape maintenance in the etching process. Therefore, in order to achieve a highly precise processing with a thinner resist layer, it is required to provide an etching process capable of sufficiently protecting the sidewalls while mainlining a low etching rate of the resist layer, i.e., a high etching selectivity for the layer to be etched against the resist layer (resist selectivity).
In the etching process, the achievement of a high selectivity for the layer to be etched against the underlying layer (underlying layer selectivity) is essential in order to enhance the performance and reliability of the fabricated semiconductor devices. For example, in the etching to form gate electrodes, a high selectivity for the gate conductive layer against a gate oxide layer should be secured. Similarly, in silicon oxide etching to form contact holes, the selectivity against, for example, a Si substrate and a suicide layer formed on the Si substrate should be sufficiently high. Also, the selectivity against a silicon nitride etch-stop layer used in a self-alignment contact (SAC) process should be sufficiently high. Further, in via hole etching, the selectivity should be high against an underlying metal such as TiN used as an antireflection layer.
In addition, in the etching process, vertical sidewalls are not always most desirable. For example, a wiring pattern should preferably be etched in a normal taper manner in order to improve the coverage of an interlayer insulating film. Also, a contact hole or via hole should preferably be etched in a normal taper manner in order to improve the coverage of a metal wiring layer in the hole.
To achieve the satisfactory sidewall protection effect, the high resist selectivity, the high underlying layer selectivity and to control the angle of the sidewall, various etching gas atmospheres including a primary etching gas for producing a primary etchant species and a variety of additional gases have been investigated. For example, in oxide film etching using CxFy gas as a primary etching gas, it was proposed to increase the C/F ratio in the plasma. Because F radicals serving as a primary etchant species are also capable of etching an underlying layer, such as a Si substrate, the surface of the underlying layer should preferably be covered with a protective film after the etch-off of the layer to be etched. By raising the C/F ratio, a number of CF2 radicals and CF radicals, which act as precursors to form a polymer film, can be increased. A fluorocarbon protective film can be thereby formed on the exposed surface of the underlying layer. For this reason, as the primary etching gas for oxide etching, C2F6, C3F8 and other straight-chain fluorocarbons, and C4F8 and other unsaturated fluorocarbons having a large number of carbon atoms, have been used. As the additional gas, H2, CHF3, CH2F2, CH3F and other hydrogen-containing gases and CO have been used to scavenge excess fluorine in the plasma and thereby increase the C/F ratio in the plasma.
Meanwhile, in the fabrication of semiconductor devices with a design rule of 0.25 xcexcm or less, a bottom antireflection coating (BARC) is widely used to enhance the precision of photolithography process. According to the process, a BARC layer composed of an organic substance is coated under a resist layer. The BARC layer serves to planarize the substrate surface, as well as to suppress the reflection of the exposing light from the underlying layer so as to improve the precision in the photolithography process. The BARC layer is etched using oxygen radicals as a primary etchant species after the development of the resist pattern. A layer to be etched is then etched using the resist pattern and BARC pattern as a mask. A dry etching technique may also be applied in developing the resist layer in the future. For instance, the surface of the resist is treated with a silylating agent such as hexamethyldisilazane (HMDS) before or after the photoexposure. A patterned silylated surface layer, which is resistant to oxygen plasma, is formed. And the resist in un-silylated regions are removed by reactive ion etching (RIE) using oxygen as a primary etching gas.
The above-mentioned conventional etching processes for use in the production of semiconductor devices have, however, the following disadvantages.
Etching is performed in various discharging types, such as reactive ion etching (RIE), magnetron enhanced reactive ion etching (MERIE), electron cyclotron resonance (ECR), and helicon-wave etching, and electron energy in one discharging type is different from that in another type. Further, a compound molecule has a specific dissociation energy. Accordingly, the etchant gas must be selected in accordance with the type of the etching system. Dissociation of a molecule cannot be significantly controlled with a high precision even if a suitable gas species for each etching system is selected. Therefore, in silicon oxide etching, a CxFy gas cannot be controllably decomposed to obtain a sufficient amount of CF2 radicals and/or CF radicals. The use of a gas having a high C/F ratio is preferred to improve the selectivity. However, the use of a gas having a high C/F ratio invites, for example, a decreased etching rate, difficulty in removal of the resist pattern after etching, and an increased contact resistance due to carbon implantation into the substrate surface.
Specifically, when a gas having a high C/F ratio is used, the etching rate is reduced due to a polymer film formed on the surface of the layer to be etched. If the discharging power is increased to compensate for such reduction in etching rate, CF2 radicals and/or CF radicals are further dissociated to increase the amount of fluorine atoms. As a result, the underlying layer selectivity is sacrificed although the etching rate can be raised. As thus described, conventional gas systems, which are mainly directed to forming CF2 radicals and/or CF radicals and to polymerizing the same, cannot yield a high resist and/or underlying layer selectivity while concurrently fulfilling other requirements.
In the BARC etching process, oxygen radicals serving as a primary etchant species etch the resist and BARC in a relatively isotropic manner, resulting in a loss of critical dimension (CD). A possible solution to the CD loss is to increase the substrate bias voltage. Ions accelerated by the substrate bias bombard the resist layer and organic species sputtered from the resist layer adhere on the sidewalls, thereby forming a protective film. Excessive adherence of the resist ingredients, however, causes a remarkable CD gain. Also, shoulders of the resist patterns facet and cause abnormal shapes of the etched layer, such as facets in the shoulders.
As thus described, the etching process proceeds with a delicate balance between various factors. Therefore, a high etching rate cannot be obtained concurrently with a satisfactory sidewall protection according to the conventional etching processes. The conventional processes havetherefore disadvantages, such as a low productivity and a large dimensional change depending on the density of the patterns.
In order to develop a resist layer by dry etching, the etching should be performed on a resist layer having a larger thickness than the BARC layer. Conventional etching processes cannot be applied to the resist development with a sufficient precision and productivity necessary for the mass production of semiconductor devices.
The present invention has been accomplished to solve the problems inherent in the conventional technologies, and it is an object of the invention to provide an etching method, which can yield a satisfactory sidewall protection concurrently with an improved resist and/or underlying layer selectivity.
According to one aspect of the invention, an exemplary method for forming a gate electrode of a semiconductor device comprises providing a semiconductor substrate having a stack of a resist mask layer, an organic coating layer, a conductive material layer, and a gate dielectric layer, the resist mask layer including a resist mask pattern partially masking the organic coating layer; etching the organic coating layer through the resist mask layer using an etching gas atmosphere including an oxygen-containing gas, a chlorine-containing gas, and a bromine-containing gas to form a pattern of the organic coating corresponding with the resist mask pattern, a width of the resist mask pattern is reduced during the etching of the organic coating layer, and a width of the pattern of the organic coating is determined by the reduced width of the resist mask pattern; and patterning the conductive material layer by etching through the pattern of the organic material.
Preferably, an amount of overetching in the etching is selected so that a desired amount of reduction of the width of the resist mask pattern is obtained.
Preferably, the oxygen-containing gas is O2. Further preferably, the chlorine-containing gas is Cl2 and the bromine-containing gas is hydrogen bromide.
Preferably, the organic coating layer is a bottom anti reflection coating (BARC) layer. The conductive material layer preferably includes a polycrystalline silicon layer.
According to another aspect of the invention, an exemplary method for manufacturing a semiconductor device comprises providing a semiconductor substrate having an organic material layer thereon and a mask layer having a mask pattern partially masking the organic material layer; and etching the organic material layer through the mask layer using an etching gas atmosphere including an oxygen-containing gas, a chlorine-containing gas, and a bromine-containing gas.
Preferably, the oxygen-containing gas is O2. Further preferably, the chlorine-containing gas is Cl2 and the bromine-containing gas is hydrogen bromide.
Preferably, the etching of the organic material layer includes substantially anisotropically etching to form a pattern of the organic material layer corresponding with the mask pattern, and laterally etching the formed pattern of the organic material layer. Preferably, a lateral dimension of the pattern of the organic material layer formed by the substantially anisotropic etching is substantially identical to a lateral dimension of the mask pattern before the etching.
Preferably, the mask pattern includes an isolated mask pattern having a first lateral mask dimension before the etching and a densely arranged mask pattern having a second lateral mask dimension before the etching; and etching the organic material layer forms an isolated pattern of the organic material layer corresponding with the isolated mask pattern and a densely arranged pattern of the organic material layer corresponding with the densely arranged mask pattern. The isolated pattern of the organic material layer has a first lateral dimension, the densely arranged pattern of the organic material layer has a second lateral dimension, and a first difference between the first pattern dimension and the first mask dimension is substantially identical to a second difference between the second pattern dimension and the second mask dimension. Preferably, a ratio of the oxygen-containing gas and the chlorine-containing gas in the etching gas atmosphere is selected so that the first difference is substantially identical to the second difference. Preferably, sidewalls of the isolated pattern have a first angle, and sidewalls of the densely arranged pattern have a second angle that is substantially identical to the first angle.
According to another aspect of the invention, an exemplary method for adjusting a lateral dimension of a resist mask pattern comprises providing a semiconductor substrate having a resist mask layer thereon, the resist mask layer including a resist mask pattern; and adjusting a lateral dimension of the resist mask pattern by laterally etching the resist using an etching gas atmosphere including an oxygen-containing gas, a chlorine-containing gas, and a bromine-containing gas.
Preferably, the oxygen-containing gas is O2. Further preferably, the chlorine-containing gas is Cl2 and the bromine-containing gas is hydrogen bromide.
Preferably, an angle of the sidewalls of the resist mask pattern after the adjusting is substantially identical to the angle of the sidewalls before the adjusting.
Preferably, the resist mask pattern include an isolated mask pattern and a densely arranged mask pattern, and an amount of the lateral etching on the isolated mask pattern during the adjusting is substantially identical to that on the densely arranged mask pattern. Preferably, the ratio of the oxygen-containing gas and the chlorine-containing gas in the etching gas atmosphere is selected so that the amount of the lateral etching on the isolated mask pattern is substantially identical to that on the densely arranged mask pattern. Preferably, the sidewalls of the isolated mask pattern after the adjusting have a first angle, and the sidewalls of the densely arranged mask pattern after the adjusting have a second angle that is substantially identical to the first angle.
According to another aspect of the invention, a exemplary method for manufacturing a semiconductor device comprises providing a semiconductor substrate having an organic material layer thereon and a mask layer having a mask pattern partially masking the organic material layer; and etching the organic material layer through the mask layer using an etching gas atmosphere including an oxygen-containing gas and one of (i) a bromide of hydrocarbon or its derivative and (ii) a combination of a bromine-containing gas and a hydrocarbon or its derivative.
Preferably, the oxygen-containing gas is O2.
Preferably, the etching gas atmosphere contains the bromide of hydrocarbon or its derivative. Preferably, the bromide of hydrocarbon or its derivative is vinyl bromide.
Preferably, the hydrocarbon is one of an alkene and an alkyne hydrocarbon.
Preferably, the amounts of bromine and carbon atoms in the etching gas atmosphere are selected such that a mole ratio of CBr4 molecules in the etching gas atmosphere, calculated assuming that all of the bromine and carbon atoms are used to form the CBr4 molecules, is between about 3 to 20 mole %.
Preferably, the mask pattern before the etching has a lateral mask dimension; the etching forms a pattern of the organic material having sidewalls and a lateral pattern dimension; the oxygen-containing gas produces oxygen radicals that isotropically etch the organic material; and the one of (i) the bromide of hydrocarbon or its derivative and (ii) the combination of the bromine-containing gas and the hydrocarbon or its derivative produces a sufficient amount of reaction product having a Cxe2x80x94Br bond to protect the sidewalls of the organic material from the oxygen radicals such that the lateral pattern dimension is substantially identical to the lateral mask dimension.
According to another aspect of the invention, an exemplary method for manufacturing a semiconductor device comprises providing a semiconductor substrate having a dielectric layer thereon, a conductive material layer covering the dielectric layer, and a mask layer including a mask pattern partially masking the conductive material layer; and etching the conductive material layer through the mask layer, the etching including a main etching for etching substantially the thickness of the conductive material layer and an overetching for removing residues of the conductive material remaining on the dielectric layer, wherein the overetching comprises using an overetching gas atmosphere including an oxygen-containing gas and one of (i) a bromide of hydrocarbon or its derivative and (ii) a combination of a bromine-containing gas and a hydrocarbon or its derivative.
Preferably, the hydrocarbon is one of an alkene and an alkyne hydrocarbon.
Preferably, the etching gas atmosphere includes the bromide of hydrocarbon or its derivative. Preferably, the bromide of hydrocarbon or its derivative is vinyl bromide.
Preferably, the overetching gas atmosphere includes the bromide of hydrocarbon or its derivative and a bromine-containing gas.
Preferably, the overetching gas atmosphere includes Br2 as the bromine-containing gas.
Preferably, the amounts of bromine and the carbon atoms in the overetching gas atmosphere are selected such that a mole ratio of CBr4 molecules in the overetching gas atmosphere, calculated assuming that all of the bromine and carbon atoms are used to form the CBr4 molecules, is between about 3 to 20 mole %.
Preferably, the overetching gas atmosphere further includes a primary etching gas that produces a primary etchant species; the etching of the residues of the conductive material is conducted primarily by the primary etchant species.
Preferably, the one of (i) the bromide of hydrocarbon or its derivative and (ii) the combination of the bromine-containing gas and the hydrocarbon or its derivative produces a sufficient amount of reaction product having a Cxe2x80x94Br bond to protect the dielectric layer during the overetching so that etching of the dielectric layer is substantially prevented compared to conducting the overetching using an overetching gas atmosphere without the one of (i) the bromide of hydrocarbon or its derivative and (ii) the combination of the bromine-containing gas and the hydrocarbon or its derivative.
According to another aspect of the invention, an exemplary method of manufacturing a semiconductor device comprises providing a semiconductor substrate having a layer of a material to be etched thereon and a mask layer including a mask pattern partially masking the material layer; and etching at least a portion of the material layer through the mask layer using an etching gas atmosphere including one of (i) a bromide of hydrocarbon or its derivative and (ii) a combination of a bromine-containing gas and a hydrocarbon or its derivative, wherein the hydrocarbon is one of an alkene and an alkyne hydrocarbon.
Preferably, the etching gas atmosphere further includes a primary etching gas that produces a primary etchant species; the etching of the material layer is primarily conducted by the primary etchant species.
Preferably, the etching gas atmosphere includes the bromide of hydrocarbon or its derivative. Preferably, the bromide of hydrocarbon or its derivative is vinyl bromide.
Preferably, the etching gas atmosphere includes Br2 as the bromine-containing gas.
Preferably, the amounts of the bromine and carbon atoms in the etching gas atmosphere are determined such that a mole ratio of CBr4 molecules in the etching gas atmosphere, calculated assuming that all of the bromine and carbon atoms are used to form the CBr4 molecules, is between about 3 to 20 mole %.
Preferably, the mask pattern has a lateral mask dimension before the etching; the etching forms a pattern of the material layer corresponding with the mask pattern, the pattern of the material layer has a lateral pattern dimension; and the one of (i) the bromide of hydrocarbon or its derivative and (ii) the combination of the bromine-containing gas and the hydrocarbon or its derivative produces a sufficient amount of reaction product having a Cxe2x80x94Br bond to protect sidewalls of the pattern of the material layer such that the lateral pattern dimension is substantially identical to the lateral mask dimension.
Preferably, the semiconductor substrate also has an underlying layer under the layer of the material to be etched and the etching of the layer is continued until the underlying layer is exposed in unmasked portions; and the one of (i) the bromide of hydrocarbon or its derivative and (ii) the combination of the bromine-containing gas and the hydrocarbon or its derivative produces a sufficient amount of reaction product having a Cxe2x80x94Br bond to protect the underlying layer so that etching of the underlying layer is substantially prevented as compared to conducting the etching using an etching gas atmosphere without the one of (i) the bromide of hydrocarbon or its derivative and (ii) the combination of the bromine-containing gas and the hydrocarbon or its derivative.